1. Field of the invention:
This invention relates to a photo chemical reaction apparatus such as a photo chemical vapor deposition apparatus, and more particularly to a photo chemical reaction apparatus using a load-lock mechanism in which a reaction chamber is sealed continuously against atmospheric pressure during the process of manufacturing semiconductors.
2. Description of the Prior Art:
In recent years, along with the progress of semiconductor integrated circuits, miniaturization and higher integration of semiconductor elements have been required. To meet these requirements, a photo excited process has become of major interest. This photo excited process is one of the low-temperature processes for manufacturing semiconductors intended to avoid possible damage caused by high-temperature processing. Hitherto, a photo chemical vapor deposition apparatus (hereinafter, simply referred to as photo CVD apparatus) has utilized the photo excited process. This apparatus includes a vacuum container in which wafers to be processed are disposed, means for introducing gases into the container, and means for applying light on the wafers through a light-penetrating window provided at a portion of the container. Application of ultraviolet rays or the like causes the surface of the wafers to be excited together with gases. This excitement achieves deposition of CVD films on the wafers.
However, in a photo CVD apparatus, while CVD films are being deposited on the wafers to be processed, the same thin film is inevitably being deposited also on the lightpenetrating window. The thin film deposited on this window causes a decrease in the amount of incident light into the vacuum container. Thus, the film growth rate of the CVD films on the wafers decreases significantly. In order to solve this problem, two countermeasures have been considered. In one technique, oil of a fluorine group is applied to the light-penetrating window prior to the processing. In the other technique, so-called "purging", in which N.sub.2 gas is blown on the window, is carried out.
However, such oil is apt to be mixed into the CVD film as an impurity. Further, the deposition of thin films on the window cannot be completely prevented even after the oil is applied to the window. Moreover, to achieve proper blowing of N.sub.2 gas, the window should have minute holes from which N.sub.2 gas flows out. This flow creates a layer flow of N.sub.2 gas on the surface of the window. The flow of N.sub.2 gas may also be created in the lateral direction on the window surface. However, the flow inevitably requires a window of complicated construction. In addition, the gas is diluted with such flow of N.sub.2 gas. Thus, the growth rate of deposition decreases.
For example, in the case of the mass production of amorphous silicon devices, the deposition of amorphous silicon film on the window cannot be sufficiently prevented even when the oil of a fluorine group is applied to the window. Further, unlike other insulating films, the amorphous silicon film absorbs a large amount of light. Specifically, while the CVD film of amorphous silicon of about 3 .mu.m thickness is created on the wafer, an amorphous silicon film of about 200 to 300 .ANG. is inevitably deposited on the window even after the oil is applied thereto. This deposition on the window causes a decrease in the amount of light of about 20%.
These phenomena are disadvantageous, particularly to the mass production of semiconductor elements for which thick films are indispensable. Moreover, in order to clean the film-deposited window, a reaction chamber must be opened to atmospheric pressure after completion of each single batch processing. This opening to atmospheric pressure for each batch causes significant problems in manufacturing semiconductor elements having a multi-layer configuration.
As described above, in the conventional photo CVD apparatus, there have been problems in that the thin film deposited on the light-penetrating window causes a decrease in the amount of incident light. Thus, the rate of film formation decreases significantly. Therefore, continuous formation of the CVD film by use of the load-lock mechanism cannot be realized. Further, these disadvantages have become serious problems not only in the photo CVD apparatus, but also in a photo etching apparatus, for example.